In the design of cooking appliances, such as toasters and toaster ovens, each different feature requires a component and interface in the control circuit. In order to produce a line of products in a particular category, it is necessary to have many different control circuits. This makes the production of the appliance more complex and adds to labor costs. It would be desirable to construct an integrated circuit module which is adaptable across a product line to provide the differing features including the necessary component and interface of each feature.
The basic feature of a control circuit for a toaster/oven type of appliance, is the control of the temperature in the cooking cavity. Cavity temperature is generally controlled by adjusting the timing of the power to the heating elements.
In toasters, the basic circuit of the control system used to adjust toasting time consists of a power supply, an oscillator, a counter, and a transistor switch. This is used to activate an on/off solenoid switch or relay which controls the power to the toaster heating elements. Adjustment is accomplished by varying the time constant of the oscillator. The oscillator is generally an RC network having a manually variable resistor. By raising the frequency of the oscillator, the time in which the counter will respond and trigger the transistor switch is reduced.
Adjustment of the resistance of the RC network is accomplished by a manually adjustable potentiometer which is set by the user. Other automatic means can be provided which responds to the temperature in the toasting cavity.
A control system of this type is shown in U.S. Pat. No. 5,402,708. This system utilizes a heat sensitive resistor to monitor and react to the residual heat accumulated by repetitive toasting cycles. A thermistor is used which performs its task by reduction of its resistance as the heat increases. Since this is a resistor which forms part of the RC network, a reduced period for the oscillator results. This translates into a shorter toasting cycle.
The broiler or oven operation is either timed by a mechanical timer or left on until interrupted by the user. In the either instance, there is a need for a safety shutoff after a reasonable time.
Other functions of a more general nature are: audible signals indicating predetermined events such as shut off, change of mode, timer expiration, etc.; voltage fluctuation compensation; additional timing sensitivity to retained heat from cycle to cycle; operational mode selection; and overall on and off actuation. It is the purpose of this invention to provide a universal toaster oven appliance control module that will allow, in conjunction with other components, many of the functions described above.